1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays].
2. Description of the Prior Arts
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as a-Si] has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 an application of a-Si for use in a photoconverting reading device.
However, under the present situation, while the photoconductive members having photoconductive layers constituted of a-Si have been attempted to be improved in various aspects individually including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with lapse of time and durability, there remains room for further improvement of overall characteristics.
For instance, when applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, a-Si has a relatively smaller coefficient of absorption in the wavelength region longer than the longer wavelength region as compared with the shorter wavelength region of the visible light region and, in matching to the semiconductor laser practically applied at present time, when using a conventionally used halogen lamp or fluorescent lamp, there remains room for improvement in that the light on the longer wavelength side cannot effectively used.
As another disadvantage, if the light irradiated cannot sufficiently be absorbed but the amount of light reaching the support is increased, when the support itself has a high reflectance against the light transmitted through the photoconductive layer, interference by multiple reflection occurs in the photoconductive layer, which may become a cause for generation of "unfocused" image.
This effect is greater as the irradiated spot is made smaller for the purpose of enhancing resolution, posing a great problem particularly when using a semiconductor laser as the light source.
On the other hand, it is also proposed to provide a light receiving layer constituted of an amorphous material containing at least germanium atoms on a support in consideration of matching to a semiconductor laser. In this case, however, problems may sometimes be ensued with respect to adhesion between the support and the above light receiving layer, and diffusion of impurities from the support to the light receiving layer.
Alternatively, in the case of constituting a photoconductive layer of a-Si material, other atoms such as hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. are contained in the photoconductive layer for improving their electrical, photoconductive characteristics; boron atoms, phosphorus atoms, etc. for controlling the electroconductivity; and other atoms for improving other characteristics as constituent atoms, respectively. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical, photoconductive characteristics or dielectric strength.
For example, when used as an image forming member for electrophotography, the life of the photocarriers generated by light irradiation in the photoconductive layer formed is insufficient, or at the dark portion, the charges injected from the support side cannot sufficiently be impeded, or there occurs image defects commonly called as "white dropout" on the images transferred on a transfer paper which may be considered to be due to the local discharge destroying phenomenon, or so called image defects commonly called as "white streaks", which may be considered to be caused by, for example, scraping with a blade employed for cleaning. Also, when used in a highly humid atmosphere or immediately after being left to stand in a highly humid atmosphere for a long time, so called "unfocused" image was frequently observed.
Thus, it is required in designing of a photoconductive material to make efforts to solve all of the problems as mentioned above along with the improvement of a-Si materials per se.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state image pick-up devices, reading devices, etc. It has now been found that a photoconductive member having a photoconductive layer comprising an amorphous layer exhibiting photoconductivity, which is constituted of a-Si, particularly so called hydrogenated amorphous silicon, halogenated amorphous silicon or halogen-containing hydrogenated amorphous silicon which is an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atoms [hereinafter referred to comprehensively as a-Si(H,X)], said photoconductive member being prepared by designing so as to have a specific structure, is found to exhibit not only practically extremely excellent characteristics but also surpass the photoconductive members of the prior art in substantially all respects, especially markedly excellent characteristics as a photoconductive member for electrophotography. The present invention is based on such finding.